# Two Tailed Test - A manufacturer claims that the mean lifetime

A manufacturer claims that the mean lifetime, , of its light bulbs is 49 months. The standard deviation of these lifetimes is 9 months. Seventy bulbs are selected at random, and their mean lifetime is found to be 46 months. Can we conclude, at the .01 level of significance, that the mean lifetime of light bulbs made by this manufacturer differs from 49 months?

Perform a two-tailed test. Then fill in the table below

Round to at least three decimal spaces

1. Hypothesis

2. Null Hypothesis

3. Type of Test Statistic; T Z Chi F

4. The two critical values at the .01 level of significance.

5. Can we conclude that the mean lifetime of the light bulbs made by this manufacture differs from 49 months.

Please explain as you answer. I am lost on this one.

https://brainmass.com/statistics/z-test/161050

#### Solution Summary

Step by step method for testing the hypothesis under 5 step approach is discussed here. Excel template for each problem is also included. This template can be used to obtain the answers of similar problems.